The air-fuel ratio in the exhaust gas of a direct injection internal combustion engine with an NOx storage catalytic converter in the exhaust system is of special importance for regeneration of the NOx storage catalytic converter. Modern lean burn engines operate with an excess of oxygen. In order to also be able to meet future exhaust standards despite the resulting oxides of nitrogen (NOx), NOx storage catalytic converters are used. In NOx storage catalytic converters, oxides of nitrogen can be temporarily stored in the (hyperstoichiometric) lean burn mode. The catalytic reduction thereof only succeeds in a rich (substoichiometric) exhaust gas mixture. If the absorption capacity of the NOx storage catalytic converter is exhausted, a rich (hyperstoichiometric) reducing exhaust gas mixture is set by the engine electronics. In the rich cycle the oxides of nitrogen temporarily stored in the NOx storage catalytic converter are reduced to nitrogen and hence the catalytic converter is prepared for the next storage cycle.
With conventional methods, the air-fuel ratio in the exhaust system is determined by a lambda probe in the exhaust system and is regulated by a regulator that varies the position of the centroid of heat release conversion rates and the injection amount of the total combusting fuel injection.
DE 10 2011 055 273 A1 and DE 10 2011 055 275 A1, which are incorporated herein by reference, describe methods for controlling and regulating the exhaust gas temperature of a direct injection internal combustion engine using a model. Here the optimum injection amount for a plurality of injections is determined predictively in order to be able to set the optimum temperature for the regeneration of a diesel particle filter.
DE 10 2006 015 503 A1, which is incorporated herein by reference, describes methods for regulating the injection process of a direct injection internal combustion engine, wherein the regulation causes a change of the injection profile at least during a first working cycle based on at least one parameter recorded during the first working cycle. A combustion regulator is provided that regulates the start of injection and the injection characteristic based on the centroid of combustion. The position of the centroid of combustion is generally recorded after the conversion of 50% of the injected fuel amount, even if this is not exact in relation to the integrated area of the conversion rate. Combustion chamber pressure sensors are used to determine the position of the centroid of combustion, using which the conversion rate can be determined from the combustion chamber pressure.
The temperature of the exhaust gas emanating from a direct injection internal combustion engine corresponds to the temperature after the exhaust valve or, if a turbocharger of the internal combustion engine is directly connected downstream, the temperature upstream of the turbine of the turbocharger. The temperature is usually regulated by an already known regulating method. However, with any regulating method delays to the regulation of the regulated variable occur because the same has to be initially determined or measured in order to be fed back again in the regulator's feedback loop. In order to counter the problem, WO 2009/112056 A1 proposes a temperature model of a gas in a combustion chamber of a cylinder in order to predictively determine the temperature of an exhaust gas emanating from the combustion chamber of the cylinder and to feed the same to a regulator. With the internal combustion engine described therein, an HC emission model is also provided in order to determine the HC emissions of an exhaust gas emanating from the combustion chamber. The same is used to regulate the regeneration of an exhaust cleaning system, in particular a particle filter.